Even 200 would make for a crowded game in my estimation (take that for whatever you deem it to be worth).
Having no idea what the rental for the location and other costs are I couldn't possibly comment on whether this all makes sense, but not for me. At 100-150 it'd be something I'd strongly consider, but certainly not 400. Never attended the NAE/F for the same sort of reasons.
They did one at disused theme park years ago which did look good, don't think it had nearly as many people in attendance (iirc) and I'd reckon the usable safe area would've been a fair bit bigger. Wish I'd done it tbh. Credit for securing a really awesome site to play, probably very hard to do.